1. Field of the Invention
The present invention relates to wireless communications and radio network technology. More specifically, the present invention relates to retransmission protocol in relay/mesh networks.
2. Description of the Related Art
A wireless relay network can be a multi-hop system in which end nodes, such as mobile stations (MS), subscription stations (SS), and mobile nodes (MN) are connected to the base station (BS), access point (AP), or access gateway (AG) via one or more relay station (RS) or relay node (RN). Communication traffic between the MS/SS and the BS/AP passes through and can be processed by the relay station (RS) or relay node (RN).
The 802.16 Mobile Multi-Hop Relay (MMR), a study item established in the Institute of Electrical and Electronics Engineers (IEEE) 802.16 working group, provides examples of relay networking. The MMR working group focuses on defining a network system that utilizes relays stations (RS) to extend the network coverage and/or enhance the system throughput. An exemplary relay network can include, in part, a relay station (RS), mobile station (MS), subscriber station (SS), and base station (BS).
Hybrid automatic repeat request (H-ARQ) is a scheme that combines ARQ protocols with forward-error-correcting (FEC) schemes that are generally considered to be good error-control techniques for wireless links. Different wireless technology may have different H-ARQ schemes.
In IEEE 802.16, the H-ARQ scheme is implemented as a part of the media access control (MAC) layer and can be enabled on a per-terminal basis. Two main variants of H-ARQ are supported: chase combining and incremental redundancy (IR). For IR, the physical (PHY) layer encodes the H-ARQ and generates four versions for the encoded H-ARQ attempts. Each H-ARQ attempt is uniquely identified using a H-ARQ attempt identifier (SPID). For chase combining, the PHY layer encodes the H-ARQ packet and generates only one version of the encoded packet. As a result, no SPID is required for chase combining. Thus, three retransmissions (four total transmissions) can be a default number of retransmissions.
For downlink operation, the BS can send a version of the encoded H-ARQ packet to the MS/SS. The MS/SS can attempt to decode the encoded packet on this first H-ARQ attempt. If the decoding is successful, the MS/SS can send an acknowledgement (ACK) to the BS. If the decoding is not successful, the MS/SS can send a non-acknowledgement (NAK or NACK) to the BS. In response, the BS can send another H-ARQ attempt to the MS/SS. The BS may continue to send H-ARQ attempts until the MS/SS successfully decodes the packet and sends an ACK.
The H-ARQ scheme can work well in a system without a relay station (RS) and where the H-ARQ scheme is applied directly between the BS and MS/SS. However, when a RS is introduced into the system, although H-ARQ is still implemented between the MS/SS and BS, the RS can be required to forward all the H-ARQ attempts and ACK/NAKs between the MS/SS and BS. Even when H-ARQ is used only on a per hop basis (for example, between each successive node), the additional delay for each hop can accumulate when there are multiple hops.